asyncio stream vs synchronous stream in socket communication with a react native app

[srinivasa rao pedada]

Objective is esp32 running micropython acts as a server while android app acts as a client. Before asyncio stream I am able to communicate successfully, but after switching to asyncio i fail to do so, only android app to esp32 is sucessfull but app is failing to retrieve json output ad I even tried text strings too . App side code remains unchanged.

micropython side code:

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response = {
      'error': 'invalid request',
        'status': 'retry'
 }

synchronous side:

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 conn.send('HTTP/1.1 200 OK\n')
 conn.send('Content-Type: application/json\n')
 conn.send('Connection: close\n\n')
 conn.sendall(ujson.dumps(response ))

asyncio side:

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swriter.write(ujson.dumps(response ))
await swriter.drain()

react native side:

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fetch( 'http://192.168.0.110' )
        .then(response => response.json())
        .then((responseJson) => {
            const data1 = responseJson;
               console.log('getting data from fetch', data1)
             
                   setData({ data1 });

                   onConnectionMessage(data1);
                  

               })

synchronous way I was able to retrieve the json output sent from esp32 to android app(react native), but the same code using asyncio i fail. asyncio client server code copied from peterhinch sir repository. What am I doing wrong?

[pythoncoder]

My client server code is intended as a demo of low level socket programming which I tested with client and server on the same LAN. It isn't intended to be an example of HTTP/web programming, which isn't one of my skills.

Perhaps it would be best if you posted your full code for all to review.

[srinivasa rao pedada]

asyncio basic server example code:

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import usocket as socket
import uasyncio as asyncio
import uselect as select
import ujson

class Server:

    def __init__(self, host='0.0.0.0', port=80, backlog=5, timeout=10):
        self.host = host
        self.port = port
        self.backlog = backlog
        self.timeout = timeout

    async def run(self):
        print('Awaiting client connection.')
        self.cid = 0
        asyncio.create_task(heartbeat(100))
        self.server = await asyncio.start_server(self.run_client, self.host, self.port, self.backlog)
        while True:
            await asyncio.sleep(100)

    async def run_client(self, sreader, swriter):
        self.cid += 1
        print('Got connection from client', self.cid)
        try:
            while True:
                try:
                    res = await asyncio.wait_for(sreader.readline(), self.timeout)
                except asyncio.TimeoutError:
                    res = b''
                if res == b'':
                    raise OSError
                print('Received {} from client {}'.format(ujson.loads(res.rstrip()), self.cid))
                response = {
                'error': 'invalid request',
                'status': 'retry'
                 }
                swriter.write('HTTP/1.1 200 OK\n')
                swriter.write('Content-Type: application/json\n')
                swriter.write('Connection: close\n\n')
                swriter.write(ujson.dumps(response))
                await swriter.drain()  # Echo back
        except OSError:
            pass
        print('Client {} disconnect.'.format(self.cid))
        await sreader.wait_closed()
        print('Client {} socket closed.'.format(self.cid))

    async def close(self):
        print('Closing server')
        self.server.close()
        await self.server.wait_closed()
        print('Server closed.')

server = Server()
try:
    asyncio.run(server.run())
except KeyboardInterrupt:
    print('Interrupted')  # This mechanism doesn't work on Unix build.
finally:
    asyncio.run(server.close())
    _ = asyncio.new_event_loop()

synchronous code:

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s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
s.bind(('', 80))
s.listen(5)
s.settimeout(20)
 try:
          conn, addr = s.accept()
          print('Got a connection from %s' % str(addr))
          gc.collect()
          request = conn.recv(2048)
          gc.collect()
          data = {
              'name': 'foo',
              'STATUS': 1
              }
          response = json.dumps(data)
          conn.send('HTTP/1.1 200 OK\n')
          conn.send('Content-Type: application/json\n')
          conn.send('Connection: close\n\n')
          conn.sendall(response)
      except Exception as e:
          print ("error while sending in loop 1 %s" % str(e))
      finally:
          conn.close()

Client failed to read json response in asyncio version but succeeded in synchronous version.

[srinivasa rao pedada]

got the error:

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asyncio.wait_for(sreader.readline(), self.timeout)

------> changed to

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asyncio.wait_for(sreader.read(2048), self.timeout)

. Now client is recieving json output immediately after closing the socket. Like you said its a timing issue, thank you sir